Recent developments of the 3GPP Long Term Evolution (LTE) facilitate accessing local IP based services in the home, office, public hot spot or even outdoor environments. One of the important use cases for the local IP access and local connectivity involves the direct communication between devices (e.g. D2D enabled devices, for example UEs or terminals) in close proximity (typically less than a few 10s of meters, but sometimes up to a few hundred meters) of each other.
This direct mode or device-to-device (i.e. D2D) communication enables a number of potential gains over the traditional cellular technique, because in D2D communication devices are typically much closer to one another than cellular devices that have to communicate via a cellular access point (AP, e.g., an eNB), such as:
Capacity gain: First, radio resources (e.g. OFDM resource blocks) between the D2D and cellular layers may be reused (reuse gain). Second, a D2D link uses a single hop between the transmitter and receiver points respectively the terminals or devices involved in direct communication, as opposed to the 2-hop link (or more) via a cellular AP (hop gain).
Peak rate gain: due to the proximity and potentially favorable propagation conditions high peak rates could be achieved (proximity gain).
Latency gain: When the devices (like UEs) communicate over a direct link, eNB forwarding may be unnecessary and the end-to-end latency can decrease.